Fix the podlint error (Instagram#1428)

Summary:
Pull Request resolved: Instagram#1428

We kept getting an error as the following:

```
    - ERROR | [OSX] unknown: Encountered an unknown error (The platform of the target `App` (macOS 10.11) is not compatible with `IGListSwiftKit (4.1.0)`, which does not support `macOS`.) during validation.
```

Looks like IGListSwiftKit did not support macos, wondering why this is the case here.

Potentially this error was introduced in this PR: Instagram#1388
cc natestedman who might know the context here

Reviewed By: natestedman

Differential Revision: D20036436

fbshipit-source-id: e9344c847c4be837bc43306a3128ffc87246efd5

.travis.yml

@@ -58,7 +58,10 @@ jobs:
  name: Cocoapods Lint
  # We need to pass all of the podspecs here so that Cocoapods uses the local version,
  # rather than searching the specs repository for the other specs in the repo.
- script: bundle exec pod lib lint --allow-warnings "--include-podspecs=*.podspec"
+ script: 
+ - bundle exec pod lib lint --allow-warnings "--include-podspecs=IGListSwiftKit.podspec" --platforms=ios,tvos
+ - bundle exec pod lib lint --allow-warnings "--include-podspecs=IGListKit.podspec"
+ - bundle exec pod lib lint --allow-warnings "--include-podspecs=IGListDiffKit.podspec"
 
  # Build example projects
  - &build-examples